In this paper I comment on recent recommendations that students' responsiveness to instruction (RTI) provides a basis for identification of students as learning disabled. I repeat an earlier argument (Gerber & Semmel, 1985) that teachers embedded in schools are naturally variable in their capacity to respond to differences in students' response to instruction. This fact continues to be the only logical empirical foundation for the construct of learning disability. I describe a theoretical model of instructional tolerance that indicates why standardized protocol RTI strategies, specifically, cannot be achieved at desirable scale without incurring enormous costs.